Method and apparatus for controlling ion energy distribution

ABSTRACT

Systems, methods and apparatus for regulating ion energies in a plasma chamber are disclosed. An exemplary system includes an ion-energy control portion, and the ion-energy control portion provides at least one ion-energy control signal responsive to at least one ion-energy setting that is indicative of a desired distribution of energies of ions bombarding a surface of a substrate. A controller is coupled to the switch-mode power supply, and the controller provides at least two drive-control signals. In addition, a switch-mode power supply is coupled to the substrate support, the ion-energy control portion and the controller. The switch-mode power supply includes switching components configured to apply power to the substrate responsive to the drive signals and the ion-energy control signal so as to effectuate the desired distribution of the energies of ions bombarding the surface of the substrate.

FIELD OF THE INVENTION

The present invention relates generally to plasma processing. In particular, but not by way of limitation, the present invention relates to methods and apparatuses for plasma-assisted etching and/or deposition.

BACKGROUND OF THE INVENTION

Many types of semiconductor devices are fabricated using plasma-based etching techniques. If it is a conductor that is etched, a negative voltage with respect to ground may be applied to the conductive substrate so as to create a substantially uniform negative voltage across the surface of the substrate conductor, which attracts positively charged ions toward the conductor, and as a consequence, the positive ions that impact the conductor have substantially the same energy.

If the substrate is a dielectric, however, a non-varying voltage is ineffective to place a voltage across the surface of the substrate. But an AC voltage (e.g., high frequency) may be applied to the conductive plate (or chuck) so that the AC field induces a voltage on the surface of the substrate. During the positive half of the AC cycle, the substrate attracts electrons, which are light relative to the mass of the positive ions; thus many electrons will be attracted to the surface of the substrate during the positive part of the cycle. As a consequence, the surface of the substrate will be charged negatively, which causes ions to be attracted toward the negatively-charged surface. And when the ions impact the surface of the substrate, the impact dislodges material from the surface of the substrate—effectuating the etching.

In many instances, it is desirable to have a narrow ion energy distribution, but applying a sinusoidal waveform to the substrate induces a broad distribution of ion energies, which limits the ability of the plasma process to carry out a desired etch profile. Known techniques to achieve a narrow ion energy distribution are expensive, inefficient, difficult to control, and may adversely affect the plasma density. As a consequence, these known techniques have not been commercially adopted. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.

SUMMARY OF THE INVENTION

Illustrative embodiments of the present invention that are shown in the drawings are summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the invention to the forms described in this Summary of the Invention or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents, and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims.

According to one embodiment, the invention may be characterized as a system for plasma-based processing. The system in this embodiment includes a plasma processing chamber configured to contain a plasma, a substrate support positioned within the plasma processing chamber and disposed to support a substrate, an ion-energy control portion that provides at least one ion-energy control signal responsive to at least one ion-energy setting that is indicative of a desired distribution of energies of ions at the surface of the substrate, and a controller coupled to the switch-mode power supply that provides one or more drive-control signals. In addition, a switch-mode power supply is coupled to the substrate support, the ion-energy control portion, and the controller, and the switch-mode power supply includes one or more switching components configured to apply power to the substrate responsive to the one or more drive signals and the ion-energy control signal so as to effectuate the desired distribution of the energies of ions at the surface of the substrate.

According to another embodiment, the invention may be described as a method for plasma-based processing that includes placing a substrate in a plasma chamber; forming a plasma in the plasma chamber; receiving at least one ion-energy setting that is indicative of a desired distribution of ion energies at a surface of the substrate; and controllably switching power to the substrate so as to effectuate the desired distribution of ion energies.

According to yet another embodiment, the invention may be characterized as a plasma-based processing apparatus that includes a controller coupled to the switch-mode power supply that provides one or more drive-control signals and an ion-energy control portion that provides at least one ion-energy control signal responsive to at least one ion-energy setting that is indicative of a desired distribution of energies of ions at the surface of the substrate. In addition, one or more switching components apply power to the substrate responsive to the one or more drive signals and the ion-energy control signal so as to effectuate the desired distribution of the energies of ions at the surface of the substrate.

These and other embodiments are described in further detail herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings where like or similar elements are designated with identical reference numerals throughout the several views and wherein:

FIG. 1 illustrates a block diagram of a plasma processing system in accordance with one implementation of the present invention;

FIG. 2 is a block diagram depicting a exemplary embodiment of the switch-mode power system depicted in FIG. 1;

FIG. 3 is a schematic representation of components that may be utilized to realize the switch-mode bias supply described with reference to FIG. 2;

FIG. 4 is a timing diagram depicting two drive signal waveforms;

FIG. 5 is a graphical representation of a single mode of operating the switch mode bias supply, which effectuates an ion energy distribution that is concentrated at a particular ion energy; and

FIG. 6 are graphs depicting a bi-modal mode of operation in which two separate peaks in ion energy distribution are generated.

DETAILED DESCRIPTION

An exemplary embodiment of a plasma processing system is shown generally in FIG. 1. As depicted, a plasma power supply 102 is coupled to a plasma processing chamber 104 and a switch-mode power supply 106 is coupled to a support 108 upon which a substrate 110 rests within the chamber 104. Also shown is a controller 112 that is coupled to the switch-mode power supply 106.

In this exemplary embodiment, the plasma processing chamber 104 may be realized by chambers of substantially conventional construction (e.g., including a vacuum enclosure which is evacuated by a pump or pumps (not shown)). And, as one of ordinary skill in the art will appreciate, the plasma excitation in the chamber 104 may be by any one of a variety of sources including, for example, a helicon type plasma source, which includes magnetic coil and antenna to ignite and sustain a plasma 114 in the reactor, and a gas inlet may be provided for introduction of a gas into the chamber 104.

As depicted, the exemplary plasma chamber 104 is arranged and configured to carry out plasma-assisted etching of materials utilizing energetic ion bombardment of the substrate 110. The plasma power supply 102 in this embodiment is configured to apply power (e.g., RF power) via a matching network (not shown)) at one or more frequencies (e.g., 13.56 MHz) to the chamber 104 so as to ignite and sustain the plasma 114. It should be understood that the present invention is not limited to any particular type of plasma power supply 102 or source to couple power to the chamber 104, and that a variety of frequencies and power levels may be may be capacitively or inductively coupled to the plasma 114.

As depicted, a dielectric substrate 110 to be treated (e.g., a semiconductor wafer), is supported at least in part by a support 108 that may include a portion of a conventional wafer chuck (e.g., for semiconductor wafer processing). The support 108 may be formed to have an insulating layer between the support 108 and the substrate 110 with the substrate 110 being capacitively coupled to the platforms but may float at a different voltage than the support 108.

As discussed above, if the substrate 110 and support 108 are conductors, it is possible to apply a non-varying voltage to the support 108, and as a consequence of electric conduction through the substrate 110, the voltage that is applied to the support 108 is also applied to the surface of the substrate 110.

When the substrate 110 is a dielectric, however, the application of a non-varying voltage to the support 108 is ineffective to place a voltage across the treated surface of the substrate 110. As a consequence, the exemplary switch-mode power supply 106 is configured to be controlled so as to effectuate a voltage on the surface of the substrate 110 that is capable of attracting ions in the plasma 114 to collide with the substrate 110 so as to carry out a controlled etching and/or deposition of the substrate 110.

Moreover, as discussed further herein, embodiments of the switch-mode power supply 106 are configured to operate so that there is an insubstantial interaction between the power applied (to the plasma 114) by the plasma power supply 102 and the power that is applied to the substrate 110 by the switch-mode power supply 106. The power applied by the switch-mode power supply 106, for example, is controllable so as to enable control of ion energy without substantially affecting the density of the plasma 114.

Furthermore, many embodiments of the exemplary switch-mode supply 106 depicted in FIG. 1 are realized by relatively inexpensive components that may be controlled by relatively simple control algorithms. And as compared to prior art approaches, many embodiments of the switch mode power supply 106 are much more efficient; thus reducing energy costs and expensive materials that are associated with removing excess thermal energy.

One known technique for applying a voltage to a dielectric substrate utilizes a high-power linear amplifier in connection with complicated control schemes to apply power to a substrate support, which induces a voltage at the surface of the substrate. This technique, however, has not been adopted by commercial entities because it has not proven to be cost effective nor sufficiently manageable. In particular, the linear amplifier that is utilized is typically large, very expensive, inefficient, and difficult to control.

Another technique that has been considered is to apply high frequency power (e.g., with one or more linear amplifiers) to the substrate. This technique, however, has been found to adversely affect the plasma density because the high frequency power that is applied to the substrate affects the plasma density.

In some embodiments, the switch-mode power supply 106 depicted in FIG. 1 may be realized by buck, boost, and/or buck-boost type power technologies. In these embodiments, the switch-mode power supply 106 may be controlled to apply varying levels of pulsed power to induce a potential on the surface of the substrate 110.

In other embodiments, the switch-mode power supply 106 is realized by other more sophisticated switch mode power and control technologies. Referring next to FIG. 2, for example, the switch-mode power supply described with reference to FIG. 1 is realized by a switch-mode bias supply 206 that is utilized to apply power to the substrate 110 to effectuate one or more desired energies of the ions that bombard the substrate 110. Also shown are an ion energy control component 220, an arc detection component 222, and a controller 212 that is coupled to both the switch-mode bias supply 206 and a waveform memory 224.

The illustrated arrangement of these components is logical; thus the components can be combined or further separated in an actual implementation, and the components can be connected in a variety of ways without changing the basic operation of the system. In some embodiments for example, the controller 212, which may be realized by hardware, software, firmware, or a combination thereof, may be utilized to control both the power supply 202 and switch-mode bias supply 206. In alternative embodiments, however, the power supply 202 and the switch-mode bias supply 206 are realized by completely separated functional units. By way of further example, the controller 212, waveform memory 224, ion energy control portion 220 and the switch-mode bias supply 206 may be integrated into a single component (e.g., residing in a common housing) or may be distributed among discrete components.

The switch-mode bias supply 206 in this embodiment is generally configured to apply a voltage to the support 208 in a controllable manner so as to effectuate a desired distribution of the energies of ions bombarding the surface of the substrate. More specifically, the switch-mode bias supply 206 is configured to effectuate the desired distribution of ion energies by applying one or more particular waveforms at particular power levels to the substrate. And more particularly, responsive to an input from the ion energy control portion 220, the switch-mode bias supply 206 applies particular power levels to effectuate particular ion energies, and applies the particular power levels using one or more voltage waveforms defined by waveform data in the waveform memory 224. As a consequence, one or more particular ion bombardment energies may be selected with the ion control portion to carry out controlled etching of the substrate.

As depicted, the switch-mode bias supply 206 includes switch components 226′, 226″ (e.g., high power field effect transistors) that are adapted to switch power to the support 208 of the substrate 210 responsive to drive signals from corresponding drive components 228′, 228″. And the drive signals 230′, 230″ that are generated by the drive components 228′, 228″ are controlled by the controller 212 based upon timing that is defined by the content of the waveform memory 224. For example, the controller 212 in many embodiments is adapted to interpret the content of the waveform memory and generate drive-control signals 232′, 232″, which are utilized by the drive components 228′, 228″ to control the drive signals 230′, 230″ to the switching components 226′, 226″. Although two switch components 226′, 226″, which may be arranged in a half-bridge configuration, are depicted for exemplary purposes, it is certainly contemplated that fewer or additional switch components may be implemented in a variety of architectures (e.g., an H-bridge configuration).

In many modes of operation, the controller 212 (e.g., using the waveform data) modulates the timing of the drive-control signals 232′, 232″ to effectuate a desired waveform at the support 208 of the substrate 210. But this is not required and in other modes of operation the timing of the drive-control signals 232′, 232″ may be constant or constant for many cycles. In addition, the switch mode bias supply 206 is adapted to supply power to the substrate 210 based upon an ion-energy control signal 234, which may be a DC signal or a time-varying waveform. Thus, the present embodiment enables control of ion distribution energies by controlling timing signals to the switching components and controlling the power (controlled by the ion-energy control component 220) that is applied by the switching components 226′, 226″.

In addition, the controller 212 in this embodiment is configured, responsive to an arc in the plasma chamber 204 being detected by the arc detection component 222, to carry out arc management functions. In some embodiments, when an arc is detected the controller 212 alters the drive-control signals 232′, 232″ so that the waveform applied at the output of the switch mode bias supply 236 extinguishes arcs in the plasma 214. In other embodiments, the controller 212 extinguishes arcs by simply interrupting the application of drive-control signals 232′, 232″ so that the application of power at the output 236 of the switch-mode bias supply 206 is interrupted.

Referring next to FIG. 3, it is a schematic representation of components that may be utilized to realize the switch-mode bias supply 206 described with reference to FIG. 2. As shown, the switching components T1 and T2 in this embodiment are arranged in a half-bridge (also referred to as or totem pole) type topology. Collectively, R2, R3, C1, and C2 represent a plasma load, and C3 is an optional physical capacitor to prevent DC current from the voltage induced on the surface of the substrate or from the voltage of an electrostatic chuck (not shown) from flowing through the circuit. As depicted, L1 is stray inductance (e.g., the natural inductance of the conductor that feeds the power to the load). And in this embodiment, there are three inputs: Vbus, V2, and V4.

V2 and V4 represent drive signals (e.g., the drive signals 230′, 230″output by the drive components 228′, 228″ described with reference to FIG. 2), and in this embodiment, V2 and V4 can be timed (e.g., the length of the pulses and/or the mutual delay) so that the closure of T1 and T2 may be modulated to control the shape of the voltage output at Vout, which is applied to the substrate support. In many implementations, the transistors used to realize the switching components T1 and T2 are not ideal switches, so to arrive at a desired waveform, the transistor-specific characteristics are taken into consideration. In many modes of operation, simply changing the timing of V2 and V4 enables a desired waveform to be applied at Vout.

For example, the switches T1, T2 may be operated so that the voltage at the surface of the substrate 110, 210 is generally negative with periodic voltage pulses approaching and/or slightly exceeding a positive voltage reference. The value of the voltage at the surface of the substrate 110, 210 is what defines the energy of the ions, which may be characterized in terms of an ion energy distribution function (IEDF). To effectuate desired voltage(s) at the surface of the substrate 110, 210, the pulses at Vout may be generally rectangular and have a width that is long enough to induce a brief positive voltage at the surface of the substrate 110, 210 so as to attract enough electrons to the surface of the substrate 110, 210 in order to achieve the desired voltage(s) and corresponding ion energies.

Vbus in this embodiment defines the amplitude of the pulses applied to Vout, which defines the voltage at the surface of the substrate, and as a consequence, the ion energy. Referring briefly again to FIG. 2, Vbus may be coupled to the ion energy control portion, which may be realized by a DC power supply that is adapted to apply a DC signal or a time-varying waveform to Vbus.

The pulse width, pulse shape, and/or mutual delay of the two signals V2, V4 may be modulated to arrive at a desired waveform at Vout, and the voltage applied to Vbus may affect the characteristics of the pulses. In other words, the voltage Vbus may affect the pulse width, pulse shape and/or the relative phase of the signals V2, V4. Referring briefly to FIG. 4, for example, shown is a timing diagram depicting two drive signal waveforms that may be applied to T1 and T2 (as V2 and V4) so as to generate the Vout signal as depicted in FIG. 4. To modulate the shape of the pulses at Vout (e.g. to achieve the smallest time for the pulse at Vout, yet reach a peak value of the pulses) the timing of the two gate drive signals V2, V4 may be controlled.

For example, the two gate drive signals V2, V4 may be applied to the switching components T1, T2 so the time that each of the pulses is applied at Vout may be short compared to the time T between pulses, but long enough to induce a positive voltage at the surface of the substrate 110, 210 to attract electrons to the surface of the substrate 110, 210. Moreover, it has been found that by changing the gate voltage level between the pulses, it is possible to control the slope of the voltage that is applied to Vout between the pulses (e.g., to achieve a substantially constant voltage at the surface of the substrate between pulses). In some modes of operation, the repetition rate of the gate pulses is about 400 kHz, but this rate may certainly vary from application to application.

Although not required, in practice, based upon modeling and refining upon actual implementation, waveforms that may be used to generate the desired ion energy distributions may be defined, and the waveforms can be stored (e.g., in the waveform memory portion described with reference to FIG. 1 as a sequence of voltage levels). In addition, in many implementations, the waveforms can be generated directly (e.g., without feedback from Vout); thus avoiding the undesirable aspects of a feedback control system (e.g., settling time).

Referring again to FIG. 3, Vbus can be modulated to control the energy of the ions, and the stored waveforms may be used to control the gate drive signals V2, V4 to achieve a desired pulse amplitude at Vout while minimizing the pulse width. Again, this is done in accordance with the particular characteristics of the transistors, which may be modeled or implemented and empirically established. Referring to FIG. 5, for example, shown are graphs depicting Vbus versus time, voltage at the surface of the substrate 110, 210 versus time, and the corresponding ion energy distribution.

The graphs in FIG. 5 depict a single mode of operating the switch mode bias supply 106, 206, which effectuates an ion energy distribution that is concentrated at a particular ion energy. As depicted, to effectuate the single concentration of ion energies in this example, the voltage applied at Vbus is maintained constant while the voltages applied to V2 and V4 are controlled (e.g., using the drive signals depicted in FIG. 3) so as to generate pulses at the output of the switch-mode bias supply 106, 206, which effectuates the corresponding ion energy distribution shown in FIG. 5.

As depicted in FIG. 5, the potential at the surface of the substrate 110, 210 is generally negative to attract the ions that bombard and etch the surface of the substrate 110, 210. The periodic short pulses that are applied to the substrate 110, 210 (by applying pulses to Vout) have a magnitude defined by the potential that is applied to Vbus, and these pulses cause a brief change in the potential of the substrate 110, 210 (e.g., close to positive or slightly positive potential), which attracts electrons to the surface of the substrate to achieve the generally negative potential along the surface of the substrate 110, 210. As depicted in FIG. 5, the constant voltage applied to Vbus effectuates a single concentration of ion flux at particular ion energy; thus a particular ion bombardment energy may be selected by simply setting Vbus to a particular potential. In other modes of operation, two or more separate concentrations of ion energies may be created.

Referring next to FIG. 6, for example, shown are graphs depicting a bi-modal mode of operation in which two separate peaks in ion energy distribution are generated. As shown, in this mode of operation, the substrate experiences two distinct levels of voltages and periodic pulses, and as a consequence, two separate concentrations of ion energies are created. As depicted, to effectuate the two distinct ion energy concentrations, the voltage that is applied at Vbus alternates between two levels, and each level defines the energy level of the two ion energy concentrations.

Although FIG. 6 depicts the two voltages at the substrate 110, 210 as alternating after every pulse, this is certainly not required. In other modes of operation for example, the voltages applied to V2 and V4 are switched (e.g., using the drive signals depicted in FIG. 3) relative to the voltage applied to Vout so that the induced voltage at surface of the substrate alternates from a first voltage to a second voltage (and vice versa) after two or more pulses.

In prior art techniques, attempts have been made to apply the combination of two waveforms (generated by waveform generators) to a linear amplifier and apply the amplified combination of the two waveforms to the substrate in order to effectuate multiple ion energies. This approach, however, is much more complex then the approach described with reference to FIG. 6, requires an expensive linear amplifier, and waveform generators.

Thus embodiments of the switch mode power supply 106, 206 provide a simple, cost effective, and efficient approach to generate a narrow ion energy distribution at one or more ion energy levels by modulating the level of voltage that is switched to the substrate 110, 210, and in many modes of operation, controlling the timing of the signals applied to the switches.

In conclusion, the present invention provides, among other things, a method and apparatus for selectively generating ion energies using a switch-mode power supply. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use, and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications, and alternative constructions fall within the scope and spirit of the disclosed invention. 

What is claimed is:
 1. A system for plasma-based processing, comprising: a plasma processing chamber configured to contain a plasma; a substrate support positioned within the plasma processing chamber and disposed to support a dielectric or semiconductor substrate, an ion-energy control portion, the ion-energy control portion including a controllable DC voltage source to provide a DC output voltage with a magnitude that is determined by an ion-energy control setting, wherein the magnitude of the DC output voltage of the DC voltage source establishes a corresponding single concentration of a particular ion-energy at the surface of the substrate; a switch-mode power supply coupled to the substrate support and the ion-energy control portion, the switch-mode power supply including at least two switching components, a first of the at least two switching components switchably connects the DC output voltage to the substrate support to provide the DC output voltage as a sole source of power that establishes the particular ion-energy at the surface of the substrate, and a second of the at least two switching components switchably connects a ground potential to the substrate support, wherein the at least two switching components are arranged in a configuration selected from the group consisting of a half-bridge configuration and a full-bridge configuration; a controller electrically coupled to each of the first and second of the at least two switching components of the switch-mode power supply by a corresponding one of a first and second drive-control-signal lines, the controller configured to provide a first and second drive-control signals, respectively, to separately open and close the first and second of the at least two switching components and control a timing of the drive-control signals to alternately switch the DC output voltage and the ground potential to the substrate support to produce a substantially constant negative voltage at the surface of the substrate between positive voltage pulses to effectuate the single concentration of desired ion energy at the surface of the substrate; and a waveform memory, the waveform memory programmed to include timing information for the drive-control signals.
 2. The system of claim 1, including a plasma power supply configured to apply power at one or more frequencies to the plasma processing chamber so as to ignite and sustain the plasma.
 3. The system of claim 1, including an arc detection component, the arc detection component detecting an indication of an arc and provide an arc signal to the controller responsive to the indication of the arc.
 4. A plasma-based processing apparatus, comprising: a controllable DC voltage source to provide a DC output voltage with a magnitude that is determined by an ion-energy control setting; at least two switching components, the at least two switching components disposed between the DC voltage source and an output that is configured to couple to a substrate holder, a first of the at least two switching components switchably connects the DC output voltage to the output to provide DC power as a sole source of power to the output, and a second of the at least two switching components switchably connects a ground potential to the output, wherein the at least two switching components are arranged in a configuration selected from the group consisting of a half-bridge configuration and a full-bridge configuration; a controller electrically coupled to each of the first and second of the at least two switching components, the controller configured to provide a first and second separate drive-control signals, respectively, to the first and second of the at least two switching components by a corresponding one of a first and separate second drive-control-signal lines and control a timing of the drive-control signals to alternately switch the DC voltage and the ground potential to the output to generate a particular voltage waveform, which when applied to a dielectric or semiconductor substrate on the substrate holder, produces a substantially constant negative voltage at the surface of the substrate between positive voltage pulses, the substantially constant negative voltage effectuates the single concentration of desired ion energy; and a waveform memory, the waveform memory programmed to include timing information for the drive-control signals.
 5. The plasma-based processing apparatus of claim 4, wherein the at least two switching components include one or more field effect transistors.
 6. The plasma-based processing apparatus of claim 4, wherein the controller includes a controller selected from the group consisting of an FPGA, a digital signal processor, a digital controller, and a processor. 